Porta Potties!--now THIS is a subject dear to my heart.
As I prefer my gear to be flexible & not built in for the sort
of travel I do, I bought for last year's travel thru Mexico an
inexpensive potty for under $20.  It's nothing more than the
classic 5 gal bucket with a snap on seat/lid.  It has the advantage of
"discretion."
 It's called a "Luggable Loo"--& after a winter's
travel use, I've renamed it my "Huggable Loo!"
 It is the best piece of gear imaginable.
I bought a couple bottles of envirnonmentally friendly toilet chemical to
use with it, & for a woman, especially, it can't be beat!
Amazingly enough, I found that not once did it tip over, even thru thousands
of miles of winding, mountainous roads, placed on the floor behind the
passenger seat.  Now, for those of you with a cabinet there, another spot
must be found.  But for me, this location, was most convenient.  At night,
when I was tucked into my lovely upper berth, I would place a shallow
plastic paint bucket atop the "loo"--which served as my "sink."
I can't say how many time, driving on long stretches of highways or
backroads, where privacy for women is an issue, I didn't hesitate to pull
over & make us of it when needed.
The "Luggable/Huggable  Loo"--& no embarrassment carrying it into gas
stations to dump...
Phaedra